After showing in a rigorous manner that when the chromatographic model is adopted to describe displacement development phenomena, HETP is twice as big as HETP in the countercurrent resin-solution model analogous to the distillation model, different equations are given for the steady-state profile according to the origin of the plates: origin where the molar fraction is 0.5, origin at the point of initial molar fraction, and origin at the middle of the band. The distance from the middle of the band to the initial molar fraction zone is given as well as molar fractions at the ends of the band.